1. Field of the Disclosure
This disclosure relates generally to a photoconductive semiconductor fiber antenna and, more particularly, to a photoconductive semiconductor fiber antenna that includes a semiconductor core and an outer cladding layer, where the cladding layer receives an optical pump beam that propagates down the cladding layer to be absorbed by the core and generate photo-carriers.
2. Discussion of the Related Art
There are situations and conditions where it is desirable to transmit and receive RF signals from a physical location without employing an antenna that can be detected at the location. Antennas are typically fabricated from electrically conducting wires or other components, and as such, will reflect incident electromagnetic waves, such as those from search radar beams. The magnitude of the radar reflectivity of a structure is referred to as its radar cross-section (RCS), and a considerable effort has been devoted to the reduction and control of a structure's RCS for various military platforms. For these situations in general, it would be desirable to transmit and receive electro-magnetic (EM) waves from a non-conductive antenna device. Unfortunately, the transmission of EM waves requires an oscillating current flow in a conductor. A next best approach is to provide an antenna structure that can be effectively turned on and off. That is the goal for the extensive research into plasma antennas, well known to those skilled in the art.
A conventional plasma antenna is essentially a structure that includes an electrical or RF discharge in a gas provided within a dielectric tube that renders the gaseous column in the tube electrically conductive by the presence of free electrons and ions. As an electrical conductor, the dielectric tube can also support RF currents impressed thereon by a transmitter or as a result of an incident received signal. Potential commercial applications for plasma antennas include a reconfigurable plasma antenna or a beam scanned array for communications systems. Although a plasma antenna provides a conductive structure that can be detected by search beams, the plasma antenna has the ability to be switched off when not in use, where it is non-conductive and thus undetectable. However, plasma antennas typically have a significant RF emission when they are active that provides a background noise that limits the sensitivity of the antenna for receiving low intensity signals. Also, plasma antennas require a heavy power source for operation.
Non-linear polycrystalline fibers are known in the art. One approach for developing such a polycrystalline fiber includes preparing a composite optical fiber preform that can be drawn into an optical fiber using a conventional fiber drawing tower, but which has a central core comprising a polycrystalline or single crystal material. To fabricate this composite perform, a hole is drilled in a fused silica preform and a single crystal or ceramic rod is precision fit into the hole. One crystalline core fiber of great interest includes a crystalline semiconductor core, such as silicon or germanium, useful for Raman applications in the millimeter-wave and infrared wavelengths. This process has created an engineered optical fiber that has significant nonlinear optical applications, but another potential application involves its application as a photoconductive fiber. It has also been proposed in the art to use crystalline semiconductor core fibers as Raman amplifiers.